About ocurrences problem

[nick048]

Hi to All,

Foollowing Your suggestion, I have written this code:

#include <stdio.h>
#include <string.h>
#include <malloc.h>

#define BUFLEN 100

struct node
{
char info[BUFLEN] ;
struct node *pun ;
} ;

typedef struct node* newlist ;

void insert_myString (newlist *test, const char *buf);
int wordCounter(char *a, char *b);

int main( void )
{
char myString1[ ] = "this is the first string and after is the
second string";
char myString2[ ] = "this is the second string";
char myString3[ ] = "this is the third string; no strings after
this string";
newlist mytest = NULL ;
char myWord[ ] = "string";
int counter = 0;
int n = 0;

insert_myString(&mytest, myString1) ;
insert_myString(&mytest, myString2) ;
insert_myString(&mytest, myString3) ;

while (mytest != NULL)
{
counter = wordCounter(mytest->info, myWord);
n = n + counter;
mytest = mytest->pun ;
}
printf("The occurrences number of word 'string' in the entire
struct is: %d\n", n);
sleep(3);
}

void insert_myString(newlist *test, const char *buf)
{
struct node *prec = *test ;

// create element
struct node *p = (newlist) malloc(sizeof(struct node)) ;

if (p == NULL) {
fprintf(stderr, "Error: memory allocation\n" ) ;
exit(-1) ;
}

strcpy(p->info, buf) ;
p->pun = NULL ; // init of last element

// the list is empty
if (prec == NULL)
*test = p ;
else {
while (prec->pun != NULL)
prec = prec->pun ;

prec->pun = p ;
}
}

int wordCounter(char *a, char *b)
{
int cnt = 0;
char *sptr = a;

while ( *sptr != '\0' && ( sptr = strstr( sptr, b ) ) != NULL )
{
cnt++;
sptr += strlen( b );
}
return(cnt);
}

After I have compiled the program and it's work fine.

Now, I have inserted the same solution in a my little server program
(sorry for the lenght)

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <errno.h>
#include <malloc.h>

#define MYPORT 10000
#define MAXCONN 5
#define BUFLEN 100

struct node
{
char info[BUFLEN] ;
struct node *pun ;
} ;

typedef struct node* newlist ;

typedef int Boolean;

/* Prototype */
void insertList (newlist *test, const char *buf);
int occurr_counter(newlist p, const char *buf);
int word_counter(char *a, const char *b);

int main(int argc, char *argv[])
{
struct sockaddr_in myServer, Client;
int socketfd, newsocketfd, client_len, char_recv, i, n, occur;
newlist newtest = NULL ;
char c;
char myString[BUFLEN];
char myWord[20];
Boolean done = 0;
char terminator[3]={'.','.','\n'};

/* local socket descriptor */
if ((socketfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
perror("system call socket failed");
exit(1);
}

memset ( &myServer, 0, sizeof(myServer) );

myServer.sin_family = AF_INET;
myServer.sin_addr.s_addr = htonl(INADDR_ANY);
myServer.sin_port = htons(MYPORT);

if (bind(socketfd, (struct sockaddr*) &myServer, sizeof(myServer))
== -1) {
perror("system call bind failed");
exit(2);
}

listen (socketfd, MAXCONN);

while (1) {
client_len = sizeof(Client);
if ((newsocketfd = accept(socketfd, (struct sockaddr *)&Client,
&client_len)) < 0) {
perror("Connection accept error");
exit(3);
}
printf("Connection Opened.\r\n");
send(newsocketfd, "Wellcome!\r\n", 11, 0);
send(newsocketfd, "Send to me Your strings !\r\n", 24, 0);
send(newsocketfd, "Close the last with .. !\r\n", 34, 0);

while (!done)
{
i=0;
char_recv = recv(newsocketfd, &c, 1, 0);
while (c !='\n')
{
myString[i++]=c;
char_recv = recv(newsocketfd, &c, 1, 0);
} /* End while (c !='\n') */
myString='\0';

/* insert myString in the struct */
insertList(&newtest, myString) ;

/* Is the last ? */
if (i > 2 && memcmp(&myString[i - 3], terminator, 2) == 0)
{
done = 1;
} /* End di if */
} /* while (!done) */

/* Query myWord */
send(newsocketfd,"Wich word will You to search?\r\n",30,0);
i=0;
char_recv = recv(newsocketfd, &c, 1, 0);
while (c !='\n')
{
myWord[i++]=c;
char_recv = recv(newsocketfd, &c, 1, 0);
} /* End while (c !='\n') */
myWord='\0';

/* I search the occurrences of myWord in the entire struct */
occur = occur_counter(newtest, myWord) ;

/* Connection closed */
send(newsocketfd,"Now I close the connection\r\n",24,0);

sleep(3);

close(newsocketfd);
printf("Connection closed.\r\n");
}
}

int occur_counter(newlist p, const char *buf)
{
int n, occ;

occ = 0;
n = 0;
while (p != NULL)
{
printf("Element: %s\n",p->info);
occ = word_counter(p->info, buf);
n = n + occ;
p = p->pun ;
}
return(n) ;
}

void insertList (newlist *test, const char *buf)
{
struct node *prec = *test ;

// element creation
struct node *p = (newlist) malloc(sizeof(struct node)) ;

if (p == NULL) {
fprintf(stderr, "'allocation memory error\n" ) ;
exit(-1) ;
}

strcpy(p->info, buf) ;
p->pun = NULL ;

// the list is empty?
if (prec == NULL)
*test = p ;
else {
while (prec->pun != NULL)
prec = prec->pun ;

prec->pun = p ;
}
}

int word_counter(char *a, const char *b)
{
int cnt = 0;
char *sptr = a;

printf("%s\n", sptr);
while ( *sptr != '\0' && ( sptr = strstr( sptr, b ) ) != NULL )
{
cnt++;
sptr += strlen( b );
}

printf( "%d\n", cnt );
return(cnt);
};

I have compiled the program (used cygWin) without errors. From cygwin
I run this program and with windows telnet I send to server the same
strings of first sample.
I have tested and the server receive and store correctly the string
sended from client.

When I search the occurrences of word "string", the server return a
mistaken number for each string.

Have You an "idea" ? I hope in Your help.

Thank You and Best Regards
Gaetano

 

[Jens Thoms Toerring]

Now, I have inserted the same solution in a my little server program
(sorry for the lenght)

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <errno.h>
#include <malloc.h>

This is no standard C header and I don't think you need it if you
instead use

#define MYPORT 10000
#define MAXCONN 5
#define BUFLEN 100

struct node
{
char info[BUFLEN] ;
struct node *pun ;
} ;

typedef struct node* newlist ;

typedef int Boolean;

/* Prototype */
void insertList (newlist *test, const char *buf);
int occurr_counter(newlist p, const char *buf);
int word_counter(char *a, const char *b);

int main(int argc, char *argv[])

Since you never use argc or argv it would make more sense to
write that as

int main( void )

{
struct sockaddr_in myServer, Client;
int socketfd, newsocketfd, client_len, char_recv, i, n, occur;
newlist newtest = NULL ;
char c;
char myString[BUFLEN];
char myWord[20];
Boolean done = 0;
char terminator[3]={'.','.','\n'};

/* local socket descriptor */
if ((socketfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
perror("system call socket failed");
exit(1);
}

I am not going to comment on the part of the program that deals
with the network stuff since it's not topical here in clc.

memset ( &myServer, 0, sizeof(myServer) );

myServer.sin_family = AF_INET;
myServer.sin_addr.s_addr = htonl(INADDR_ANY);
myServer.sin_port = htons(MYPORT);

if (bind(socketfd, (struct sockaddr*) &myServer, sizeof(myServer))
== -1) {
perror("system call bind failed");
exit(2);
}

listen (socketfd, MAXCONN);

while (1) {
client_len = sizeof(Client);
if ((newsocketfd = accept(socketfd, (struct sockaddr *)&Client,
&client_len)) < 0) {
perror("Connection accept error");
exit(3);
}
printf("Connection Opened.\r\n");
send(newsocketfd, "Wellcome!\r\n", 11, 0);
send(newsocketfd, "Send to me Your strings !\r\n", 24, 0);

There are 27 chars to send, not just 24...

send(newsocketfd, "Close the last with .. !\r\n", 34, 0);

....but here only 26 instead of 34.

while (!done)
{
i=0;
char_recv = recv(newsocketfd, &c, 1, 0);
while (c !='\n')
{
myString[i++]=c;
char_recv = recv(newsocketfd, &c, 1, 0);
} /* End while (c !='\n') */

This loop creates a serious problem: if the user sends you a string
that is longer than BUFLEN-1 you will start writing past the end of
the myString array.

And there's another problem that is in part resonsible for for your
getting the word count wrong: you also store the \n (and maybe even
an additional carriage-return character) you receive from the other
side in the string. If the user enters e.g. "abcabc" and then presses
RETURN what you store is "abcabc\n".

myString='\0';

/* insert myString in the struct */
insertList(&newtest, myString) ;

/* Is the last ? */
if (i > 2 && memcmp(&myString[i - 3], terminator, 2) == 0)
{
done = 1;
} /* End di if */
} /* while (!done) */

/* Query myWord */
send(newsocketfd,"Wich word will You to search?\r\n",30,0);

There are 31 chars to be send instead of 30.

i=0;
char_recv = recv(newsocketfd, &c, 1, 0);
while (c !='\n')
{
myWord[i++]=c;
char_recv = recv(newsocketfd, &c, 1, 0);
} /* End while (c !='\n') */
myWord='\0';

And here you have the same problems as above. If the user enters
just "a" and then presses RETURN myWord will be "a\n". And
leaving the \n in the string to search for is what makes the
comparison not work as expected since the \n is in the strings
you search in only once at the very end. So the search will
always return only 0 or 1 (and 1 only if the word you're look-
ing for is at the very end of the string you search).

/* I search the occurrences of myWord in the entire struct */
occur = occur_counter(newtest, myWord) ;

/* Connection closed */
send(newsocketfd,"Now I close the connection\r\n",24,0);

There are 28 chars you need to send, not only 24.

sleep(3);

close(newsocketfd);
printf("Connection closed.\r\n");
}
}

I have compiled the program (used cygWin) without errors.

But you should have gotten a few warnings or you should increase
the warning level of your compiler...

From cygwin
I run this program and with windows telnet I send to server the same
strings of first sample.
I have tested and the server receive and store correctly the string
sended from client.

Well, except that you have additional \n characters in there, but
they are sometimes hard to see (and you may have to actually look
for them;-)
Regards, Jens

 

[Servé Laurijssen]

After I have compiled the program and it's work fine.

Now, I have inserted the same solution in a my little server program
(sorry for the lenght)

I didnt read the rest but heres probably the solution:
buffers received from server/client code are not zero terminated. use the
return values from recv etc

 

[Frodo Baggins]

Hi to All,

strcpy(p->info, buf) ;

buffer overflow again? strncpy perhaps?

Regards,
Frodo B

 

[Richard Heathfield]

Frodo Baggins said:

buffer overflow again? strncpy perhaps?

Buffer overflow is bad, so avoid copying arbitrary data into a buffer
without first ensuring that it will fit.

But arbitrary data loss is bad too.

Recommending strncpy as a not-quite-drop-in replacement for strcpy is
poor advice.

 

[Ian Collins]

Hi to All,

Foollowing Your suggestion, I have written this code:

#include <stdio.h>
#include <string.h>
#include <malloc.h>

#define BUFLEN 100

struct node
{
char info[BUFLEN] ;
struct node *pun ;
} ;

typedef struct node* newlist ;

One more point that hasn't been raised, typedefs like the one above are
seldom, if ever, a good idea. By all means use a typedef as an alias
for struct node, but not for a pointer to struct node.

// create element
struct node *p = (newlist) malloc(sizeof(struct node)) ;

See why the typedef is not a good idea? Ignoring the unnecessary
casting of malloc's return, the line above is just confusing, casting
with what appears to be a different type. Much better to write

struct node *p = malloc( sizeof *p );

While you are cleaning up the code, drop the spaces before the
semicolons, they are inconsistent and odd.